Electrostatic charge elimination for magnetic printing system

ABSTRACT

A technique and apparatus for removing electrostatically attracted magnetic toner particles from a recorded surface on which magnetic images are formed for magnetic printing. Magnetic toner powder is applied to a surface having magnetic images recorded thereon, the toner adhering to the recorded areas for subsequent transfer to a writing surface. An electrical discharge path is provided from the recording surface to discharge electrostatically attracted particles spuriously attached to the recorded surface. Spurious particles are thereby removed from the recorded surface and are not transferred to a writing surface, with a result that cleaner and more easily readable printed material is produced.

United States Patent [191 Ott et al.

[ ELECTROSTATIC CHARGE ELIMINATION FOR MAGNETIC PRINTING SYSTEM [75] Inventors: Owen J. Ott, Brookfield Center;

David W. Ginn, Newtown, both of Conn.

[73] Assignee: Data Interface, Inc., Danbury,

Conn.

I [22] Filed: May 25, 1972 [21] Appl. No.: 256,993

[11] 3,816,799 June 11, 1974 Primary ExaminerL. T. Nix Attorney, Agent, or Firm-Weingarten, Martharn {9t Schurgin [5 7] ABSTRACT A technique and apparatus for removing electrostatically attracted magnetic toner particles from a recorded surface on which magnetic images are formed for magnetic printing. Magnetic toner powder is applied to a surface having magnetic images recorded thereon, the toner adhering to the recorded areas for subsequent transfer to a writing surface. An electrical discharge path is provided from the recording surface to discharge electrostatically attracted particles spuriously attached to the recorded surface. Spurious particles are thereby removed from the recorded surface and are not transferred to a writing surface, with a result that cleaner and more easily readable printed material is produced.

5 Claims, 5 Drawing Figures TONER I .14

TRANSFER ERASE RECORDING CIRCUITRY A22 CIRCUITRY mmnmum m4 3.816799 sum 1 OF 2 I TONER 4 26 20v APPL.

PRINT TRANSFER ERASE 43 RECORDING CIRCUITRY @22 CIRCUITRY 28 ELECTROSTATIC CHARGE ELIMINATION FOR MAGNETIC PRINTING SYSTEM FIELD OF THE INVENTION This invention relates to magnetic printing systems and more particularly to apparatus and a technique for the removal of electrostatically attracted particles of magnetic toner spuriously attached to a magnetic surface along with intended toner particles for printing.

BACKGROUND OF THE INVENTION In magnetic printing systems, such as described in copending application Ser. No. 138,924, assigned to the assignee of this invention, a magnetic image is recorded on a magnetic tape or other recording medium to represent characters or other data to be printed, and magnetic toner powder is applied to the recorded areas of the tape. The toner is then transferred from the tape to a confronting writing surface to form a printed image. Toner powder is typically applied to the tape by means of a rotating brush or impeller which conveys powder from a reservoir onto the tape surface. During application of toner onto a tape surface, agitation of toner particles can cause particles to acquire an electrostatic charge, the charged particles becoming attached to the tape in areas not defined by the magnetic image. These electrostatically attached particles can produce unwanted gray background areas on the printed material when toner is transferred from the tape to the writing surface. It is an object of the present invention to provide a technique and apparatus for the substantial reduction of the number of electrostatically charged particles which can become affixed to the tape surface and which results in a significantly cleaner printed image.

SUMMARY OF THE, INVENTION In accordance with the present invention, a conductive discharge path is provided from the recording surface such that electrostatically charged particles are discharged and removed from the tape surface prior to printing. In a typical embodiment, a relatively dense mass of toner powder is provided in contact with the tape surface on which a magnetic image is formed, this mass of toner by reason of the close spacing of particles thereof having a higher electrical conductivity than the more dispersed toner powder being brushed or otherwise applied to the tape surface for attraction to the magnetically recorded image areas. The relatively high electrical conductivity of the toner mass serves to remove the electrostatic charge of particles electrostatically attracted to the tape surface, and upon being discharged the spurious particles are removed from the tape surface leaving the intended particles magnetically adhered to the recorded image areas.

In typical implementation, a toner applicator embodying the invention comprises a rotating brush disposed within a cylindrical reservoir of toner powder having an inside diameter approximating the diameter of the rotating brush. An aperture is provided past which the tape is caused to move, and the brush upon rotation is operative to apply toner from the reservoir onto the tape surface for adherance of toner particles to the recorded image areas. A shelf is provided in the aperture in a position removed from the tape surface, the shelf being operative to maintain a mass of toner powder between the shelf and confronting tape surface to provide a relatively high conductivity mass for discharge of spuriously applied toner particles. The high conductivity mass is provided at a position which confronts the tape surface subsequent to the application of toner. As the tape containing both toner affixed to the recorded areas and toner particles spuriously attached to non-recorded areas is moved past the high conductivity mass, the spurious particles become discharged and are collected by the mass. The magnetically applied particles remain on the tape surface for transfer to the writing surface.

In an alternative embodiment, the toner powder applied to the recorded areas of the tape surface, as well as the electrostatically attracted spurious particles, are moved across the confronting surface of a conductive plate which is effective to discharge the electrostatically attracted particles while the magnetically attracted particles remain adhered to the recorded tape surface for subsequent transfer to the writing surface.

DESCRIPTION OF THE DRAWINGS The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of a magnetic printing system of a type in which the invention is especially useful;

FIG. 2 is a pictorial view, partly cutaway, of a toner applicator embodying the invention; and

FIG. 3 is a cutaway elevation view of a portion of the toner application of FIG. 2;

FIG. 4 is a cutaway elevation view of an alternative toner applicator embodying the invention; and

FIG. 5 is a cutaway pictorial view of a portion of the toner applicator of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION A magnetic printing system in which the invention is especially useful is shown in diagrammatic form in FIG. 1. A magnetic tape 10 or other suitable magnetic recording medium is disposed for movement along a predetermined path in the direction indicated by arrow 12. A magnetic recording head 14 is provided in operative relation with the recording surface of tape 10 and is connected to recording circuitry 16 operative to provided recording signals to the tape for formation of magnetic images thereon representing characters or other data to be printed: A toner applicator 18 embodying the present invention is disposed in association with the recording surface of tape 10 and is operative to apply magnetic toner powder to the tape for adherance to the recorded areas thereof. Patterns of magnetic toner are thereby provided as defined by the configuration of the recorded areas, and these patterns are transferred to a writing surface to form the printed image.

A writing surface such as a paper sheet 20 is provided in juxtaposition to the surface of tape 10 containing the toner, and transfer of toner from the tape onto the writing surface is accomplished by print transfer apparatus 22 which impresses the confronting surfaces of tape 10 and sheet 20 into engagement against a platen 24. The transfer apparatus can include, for example, a helical cam which sequentially transverses the writing surface to cause transfer of a line characters from the tape onto the writing surface. Any magnetic toner particles remaining on the tape after printing are removed by a magnetic erase head 26 cooperative with erase circuitry 28. In a typical implementation, the magnetic tape is of endless loop configuration such that the tape is continually re-employed with new recorded information to be printed.

Since printing is accomplished by transfer of toner powder from the tape surface onto a writing surface, any toner particles which may spuriously be affixed to the tape surface will also be transferred. As discussed above, particles of toner being applied to the recorded tape surface can become electrostatically charged and affixed to the surface in other than the recorded areas. Transfer of these electrostatically affixed particles to the writing surface can cause a dirty or gray background on which printing occurs, with overall loss of clarity and crispness of print quality. The toner applica tor 18 includes means for substantially eliminating the problem of spurious toner particles electrostatically attracted to the tape surface.

The toner applicator is shown in FIGS. 2 and 3 and includes a housing 30 having a rectangular aperture 32 on the upper face thereof which confronts a surface of magnetic tape 10 arranged for movement past aperture 32. A cover member 34 is provided on the opposite surface of tape 10 to retain the tape in close alignment with the aperture and to prevent the release of toner particles from housing 30. The housing contains magnetic toner powder 36 and a cylindrical brush-38 rotatably disposed therein. The brush 38 includes bristles 40 affixed to a hub 42 having a shaft 44 journaled in a bearing provided in a side wall of housing 30. The shaft 44 is connected to a motor 46 or other motive means for rotation of brush 38 within the housing. The interior 'of housing 30 is cylindrical and of a diameter substantially the same as the diameter of brush 38. The ends of bristles 40 within aperture 32 are closely adjacent the confronting tape surface for application of toner particles thereto.

Upon rotation of brush 38, particles areswept from the supply within housing 30 onto the tape surface as the recorded tape moves past aperture 34. Toner particles are magnetically attracted to the recorded areas of the tape and particles not adhering to the tape fall back into the housing. A shelf 48 is provided within housing 30 in spaced apart relationship with the surface of tape 10 to which toner is being applied, and this shelf is in a position to confront the tape subsequent to the application of toner to the recorded areas thereof. A mass 50 of toner powder is supported by shelf 48 in contact with the confronting tape surface and this mass is of sufficient density to provide an electrical conductivity higher than that of the dispersed toner particles being applied to the recorded areas of tape 10.

The more highly conductive mass 50 is effective to discharge the electrostatic charge of the particles spuriously affixed to the tape, and, upon discharge, the spurious particles are removed from the tape surface and are collected as part of the mass 50. The toner applied to the magnetically recorded areas of tape 10 is not affected by the presence of mass 50 and is moved through this mass into a position for transfer onto the writing surface. By virtue of the invention, the resulting printed image is quite clean and sharp since spurious toner particles which could impair print quality are removed from the tape surface prior to imprinting of the recorded images.

An alternative embodiment of the invention is depicted in FIGS. 4 and 5 wherein the electrostatic charge of toner particles is removed by passage of the tape surface containing toner thereon past the confronting surface of a conductive plate. Referring to FIGS. 4 and 5, the tape 10 passes over a curved plate 60 provided on the top of the toner applicator housing and having a rectangular aperture 62 through which toner powder is applied to the recording surface of the tape. A recessed channel 64 is provided adjacent aperture 62 over which the tape having toner applied thereto is moved in its travel towards a printing position at which toner is transferred to a writing surface. The recessed portion 64 of plate 60 allows the passage of the mass of toner adhered to the recording surface without removal of significant amounts of the magnetically attracted toner. With the toner in contact with the conductive surface of recessed portion 64, the conductivity of the toner mass is higher than that of the dispersed particles being applied by the toner applicator to the tape surface, such that the electrostatic charges of the particles spuriously affixed to the tape are discharged to the conductive plate 60. The discharged particles fall or are wiped from the tape, and excess amounts of toner as well as the discharged particles removed from the tape fall back into the reservoir through an opening 66 provided in plate 68 which serves as a mechanical shield and which typically is formed of spring material urged into contact with the recording surface of the tape.

The rotatable toner applicator brush 70 is disposed for rotation on a hub 72 and includes bristles having tapered ends 74 which generally conform to'the curve of the apertured plate 60. An arm 76 fastened to the toner applicator housing has an edge portion 78 which is bent into engagement with the bristle ends in a portion near the aperture 62. The edge 78 is operative open rotation of brush 70 to cause a snapping or flicking of the bristles through aperture 62 and onto the recording surface in confronting relation therewith. The toner applicator brush 70 preferably engages the confronting portion 80 of the interior wall of the toner reservoir to collect toner powder within the reservoir.

A second brush 82 having diametrically opposed bristles 84 is provided within the toner applicator and is rotatable on a hub 86 driven in the same direction as that of brush 70. The bristles 84 are disposed to engage the bristle ends of brush 70 during operation to agitate the bristles of brush 70 and maintain the toner particles in a dispersed and noncompacted state. The brushes 70 and 84 are driven by a belt 88 engaging hubs 72 and 86 and which in the illustrated embodiment is formed of helical wire spring material to provide an open structure which prevents bunching and compacting of the toner powder. The hub 86 is smaller in diameter than that of hub 72 and brush 84 thus rotates at a faster rate than brush 70 and causes rapid agitation of brush 70 and the toner powder. The tape is maintained in position against the upper surface of the toner applicator by means of a pressure roller.

It is not intended to limit the invention by what has been particularly shown and described as various modifications and alternative implementations will occur to those versed in the art.

What is claimed is:

1. Apparatus for the removal of spurious magnetic tone'r particles electrostatically affixed to a surface on which magnetic images are recorded, said appartus comprising:

a housing containing a supply of magnetic toner powder and having an aperture disposed in confronting relation to a recording surface;

meansfor applying said toner powder to said recording surface to cause adherance of toner particles to magnetic recorded areas thereof; and

means for maintaining a mass of toner particles in contact with said recording surface and of a density providing an electrical conductivity sufficient to discharge spuriously attracted toner particles adhered to said recording surface by electrostatic attraction.

2. For use in magnetic printing apparatus having a surface on which magnetic recorded images are formed and an applicator for applying magnetic toner powder to recorded areas of said surface, apparatus for removing spurious toner particles electrostatically affixed to said surface and comprising:

means for maintaining a mass of toner powder in physical contact with said surface, said mass providing an electrical conductivity sufficient for discharge of the electrostatic charge of said spuriously attached particles to permit removal of said discharged particles from said recorded surface; and

means for moving said recording surface along said mass to cause discharge of electrostatically attracted particles on said surface and removal of said discharged particles from said surface.

3. A method for removing spurious electrostatically attracted magnetic toner particles from a magnetically recorded surface comprising the steps of:

applying toner particles to said recorded surface for adherence to the magnetic recorded areas thereof;

providing a mass of magnetic toner particles in contact with the recording surface, said mass being sufficient to provide an electrical conductivity higher than that of dispersed toner particles being applied to said recording surface; and

moving said recording surface having toner applied thereto past said mass to cause discharge of the electrostatically attracted particles thereof and removal of discharged particles from said recording surface.

4. Apparatus for applying magnetic toner powder to a recording surface of a magnetic recording medium, comprising:

a housing containing a supply of magnetic toner powder and having an aperture disposed in confronting relation to a recording surface;

a generally cylindrical brush mounted for rotation in said housing at a position confronting said aperture and operative to collect toner powder in said housmg;

an element supported in said housing and having an edge portion in engagement with the bristle ends of said brush and operative to cause snapping of said bristles as said brush rotates past said edge portion thereby to propel toner powder through said aperture and onto said recording surface for adherence to magnetic recorded areas thereof; and

means for providing a conductive discharge path from said recording surface operative upon movement of said recording surface containing toner particles magnetically adhered to recorded areas thereof and spurious toner particles electrostatically affixed to said surface along said means to cause discharge of said electrostatically attracted toner particles and removal of the discharged particles from said recording surface; said conductive discharge means including means for maintaining a mass of toner powder in contact with said recording surface and of a density providing an electrical conductivity sufiicient to discharge spuriously attracted toner particles adhered to said surface by electrostatic attraction.

5. Apparatus for the removal of spurious magnetic toner particles electrostatically affixed to a surface on which magnetic images are recorded, said apparatus comprising:

a housing containing a supply of magnetic toner powder and having an aperture disposed in confronting relation to a recording surface; and

means for maintaining a mass of toner particles in contact with said recording surface and of a density providing an electrical conductivity sufficient to discharge spuriously attracted toner particles adhered to said recording surface by electrostatic attraction.

i= =l *k 

1. Apparatus for the removal of spurious magnetic toner particles electrostatically affixed to a surface on which magnetic images are recorded, said appartus comprising: a housing containing a supply of magnetic toner powder and having an aperture disposed in confronting relation to a recording surface; means for applying said toner powder to said recording surface to cause adherance of toner particles to magnetic recorded areas thereof; and means for maintaining a mass of toner particles in contact with said recording surface and of a density providing an electrical conductivity sufficient to discharge spuriously attracted toner particles adhered to said recording surface by electrostatic attraction.
 2. For use in magnetic printing apparatus having a surface on which magnetic recorded images are formed and an applicator for applying magnetic toner powder to recorded areas of said surface, apparatus for removing spurious toner particles electrostatically affixed to said surface and comprising: means for maintaining a mass of toner powder in physical contact with said surface, said mass providing an electrical conductivity sufficient for discharge of the electrostatic charge of said spuriously attached particles to permit removal of said discharged particles from said recorded surface; and means for moving said recording surface along said mass to cause discharge of electrOstatically attracted particles on said surface and removal of said discharged particles from said surface.
 3. A method for removing spurious electrostatically attracted magnetic toner particles from a magnetically recorded surface comprising the steps of: applying toner particles to said recorded surface for adherence to the magnetic recorded areas thereof; providing a mass of magnetic toner particles in contact with the recording surface, said mass being sufficient to provide an electrical conductivity higher than that of dispersed toner particles being applied to said recording surface; and moving said recording surface having toner applied thereto past said mass to cause discharge of the electrostatically attracted particles thereof and removal of discharged particles from said recording surface.
 4. Apparatus for applying magnetic toner powder to a recording surface of a magnetic recording medium, comprising: a housing containing a supply of magnetic toner powder and having an aperture disposed in confronting relation to a recording surface; a generally cylindrical brush mounted for rotation in said housing at a position confronting said aperture and operative to collect toner powder in said housing; an element supported in said housing and having an edge portion in engagement with the bristle ends of said brush and operative to cause snapping of said bristles as said brush rotates past said edge portion thereby to propel toner powder through said aperture and onto said recording surface for adherence to magnetic recorded areas thereof; and means for providing a conductive discharge path from said recording surface operative upon movement of said recording surface containing toner particles magnetically adhered to recorded areas thereof and spurious toner particles electrostatically affixed to said surface along said means to cause discharge of said electrostatically attracted toner particles and removal of the discharged particles from said recording surface; said conductive discharge means including means for maintaining a mass of toner powder in contact with said recording surface and of a density providing an electrical conductivity sufficient to discharge spuriously attracted toner particles adhered to said surface by electrostatic attraction.
 5. Apparatus for the removal of spurious magnetic toner particles electrostatically affixed to a surface on which magnetic images are recorded, said apparatus comprising: a housing containing a supply of magnetic toner powder and having an aperture disposed in confronting relation to a recording surface; and means for maintaining a mass of toner particles in contact with said recording surface and of a density providing an electrical conductivity sufficient to discharge spuriously attracted toner particles adhered to said recording surface by electrostatic attraction. 